This application is based upon and claims the benefit of priority from the prior Japanese Patent Applications No. 11-262327, filed Sep. 16, 1999; No. 11-263741, filed Sep. 17, 1999; No. 2000-265663, filed Sep. 1, 2000; and No. 2000-265664, filed Sep. 1, 2000, the entire contents of which are incorporated herein by reference.
The present invention relates to a magnetoresistive element having ferromagnetic double tunnel junction, and, a magnetic memory device using the same.
The magnetoresistance effect is a phenomenon that electrical resistance changes when a magnetic field is applied to a ferromagnetic material. As the magnetoresistive element (MR element) using the above effect has superior temperature stability within a wide temperature range, it has been used for a magnetic head and a magnetic sensor, and the like. Recently, a magnetic memory device (a magnetoresistive memory or a magnetic random access memory (MRAM)) has also been fabricated. The magnetoresistive element has been required to have high sensitivity to external magnetic field and quick response.
In recent years, there has been found a magnetoresistive element having a sandwich film in which a dielectric layer is inserted between two ferromagnetic layers, and uses tunnel currents flowing perpendicularly to the film, so-called a ferromagnetic tunnel junction element (tunnel junction magnetoresistive element, TMR). The ferromagnetic tunnel junction element shows 20% or more of a change rate in magnetoresistance (J. Appl. Phys. 79, 4724 (1996)). Therefore, there has been an increased possibility to apply the TMR to a magnetic head and a magnetoresistive memory. However, there is a problem that the magnetoresistance (MR) change is considerably decreased in the ferromagnetic single tunnel junction element, when a voltage to be applied is increased to obtain required output voltage (Phys. Rev. Lett. 74, 3273 (1995)).
There has been proposed a ferromagnetic single tunnel junction element having a structure in which an antiferromagnetic layer is provided in contact with one ferromagnetic layer for the ferromagnetic single tunnel junction to make the ferromagnetic layer to be a magnetization pinned layer (Jpn. Pat. Appln. KOKAI Publication No. 10-4227). However, such an element also has a similar problem that the MR change is considerably decreased when an applied voltage is increased to obtain required output voltage.
On the other hand, there has been theoretically estimated that a magnetoresistive element having a ferromagnetic double tunnel junction forming a stacked structure of Fe/Ge/Fe/Ge/Fe has an increased MR change owing to spin-polarized resonant tunnel effect (Phys. Rev. B56, 5484 (1997)). However, the estimation is based on results at a low temperature (8K), and therefore the above phenomenon is not necessarily caused at room temperature. Note that the above element does not use a dielectric such as Al2O3, SiO2, and AlN. Moreover, as the ferromagnetic double tunnel junction element of the above structure has no ferromagnetic layer pinned with an antiferromagnetic layer, there is a problem that the output is gradually decreased owing to rotation of a part of magnetic moments in a magnetization pinned layer by performing writing several times when it is used for MRAM and the like.
In addition, there has been proposed a ferromagnetic multiple tunnel junction element comprising a dielectric layer in which magnetic particles are dispersed (Phys. Rev. B56 (10), R5747 (1997); Journal of Applied Magnetics, 23, 4-2, (1999); and Appl. Phys. LeTT. 73 (19), 2829(1998)). It has been expected that the element may be applied to a magnetic head or a magnetoresistive memory, as 20% or more of an MR change has been realized. In particular, the ferromagnetic double tunnel junction element has an advantage that the reduction in the MR change can be made low even with increased applied voltage. However, as the element has no ferromagnetic layer pinned with an antiferromagnetic layer, there is a problem that the output is gradually decreased owing to rotation of a part of magnetic moments in a magnetization pinned layer by performing writing several times when it is used for MRAM and the like. As a ferromagnetic double tunnel junction element using a ferromagnetic layer consisting of a continuous film (Appl. Phys. Lett. 73(19), 2829(1998)) has a ferromagnetic layer consisting of a single layer film of, for example, Co, Ni80Fe20 between dielectric layers, there are problems that a reversal magnetic field for reversing the magnetic moment may not be freely designed, and that coercive force of the ferromagnetic layer may be increased when the material such as Co is processed.
For application of the ferromagnetic tunnel junction element to MRAM and the like, external magnetic fields are applied to a ferromagnetic layer (free layer, or a magnetic recording layer), magnetization of which is not pinned, by flowing current in a wire (bit line or word line) in order to reverse the magnetization of the magnetic recording layer. However, since increased magnetic fields (switching magnetic fields) are required for reversing the magnetization of the magnetic recording layer as memory cells become smaller, it is necessary to flow a high current in the wire for writing. Thus, power consumption is increased for writing as memory capacity of the MRAM is increased. For example, in an MRAM device with a high density of 1 Gb or more, there may be caused a problem that the wires melt owing to increased current density for writing in the wires.
As one solution for the above problem, an attempt is made to carry out magnetization reversal by injecting spin-polarized current (J. Mag. Mag. Mat., 159 (1996) L1; and J. Mag. Mag. Mat., 202(1999) 157). However, the method for performing magnetization reversal by injection of the spin current causes increase in current density in the TMR element, which leads to destruction of a tunnel insulator. Moreover, there have been no proposals for an element structure suitable for spin injection.
An object of the present invention is to provide a magnetoresistive element of a tunnel junction type and a magnetic memory device in that reduction in the MR change can be made low even when an applied voltage is increased to obtain required output voltage, that have no problem that an output is gradually decreased owing to rotation of a part of magnetic moments in the magnetization pinned layer by repeated writing, and in that an reversal magnetic field for reversing the magnetic moments in the ferromagnetic layer can be freely designed.
Another object of the present invention is to provide a magnetoresistive element of a tunnel junction type and a magnetic memory device that can suppress increase in reversal magnetic field for reversing the magnetization of the magnetic recording layer accompanying scaling down of memory cells.
Still another object of the present invention is to provide a magnetic memory device that has a structure suitable for spin injection and can control current density in a wire and a TMR element, and a method for writing information to the magnetic memory device.
A first magnetoresistive element of the present invention comprises a ferromagnetic double tunnel junction having a stacked structure of a first antiferromagnetic layer/a first ferromagnetic layer/a first dielectric layer/a second ferromagnetic layer/a second dielectric layer/a third ferromagnetic layer/a second antiferromagnetic layer; the second ferromagnetic layer consists of a Co-based alloy, or a three-layered film of a Co-based alloy/a Nixe2x80x94Fe alloy/a Co-based alloy; and a tunnel current is flowed between the first ferromagnetic layer and the third ferromagnetic layer.
A second magnetoresistive element of the present invention comprises a ferromagnetic double tunnel junction having a stacked structure of a first ferromagnetic layer/a first dielectric layer/a second ferromagnetic layer/a first antiferromagnetic layer/a third ferromagnetic layer/a second dielectric layer/a fourth ferromagnetic layer; the first and fourth ferromagnetic layers consist of a Co-based alloy or a three-layered film of a Co-based alloy/a Nixe2x80x94Fe alloy/a Co-based alloy; and a tunnel current is flowed between the first ferromagnetic layer and the fourth ferromagnetic layer.
A third magnetoresistive element of the present invention comprises a ferromagnetic double tunnel junction having a stacked structure of a first antiferromagnetic layer/a first ferromagnetic layer/a first dielectric layer/a second ferromagnetic layer/a second antiferromagnetic layer/a third ferromagnetic layer/a second dielectric layer/a fourth ferromagnetic layer/a third antiferromagnetic layer; the first and fourth ferromagnetic layers or the second and third ferromagnetic layers consist of a Co-based alloy or a three-layered film of a Co-based alloy/a Nixe2x80x94Fe alloy/a Co-based alloy; and a tunnel current being flowed between the first ferromagnetic layer and the fourth ferromagnetic layer.
A fourth magnetoresistive element of the present invention comprises a ferromagnetic double tunnel junction having a stacked structure of a first ferromagnetic layer/a first dielectric layer/a second ferromagnetic layer/a first nonmagnetic layer/a third ferromagnetic layer/a second nonmagnetic layer/a fourth ferromagnetic layer/a second dielectric layer/a fifth ferromagnetic layer; the second, third and fourth ferromagnetic layers adjacent to each other are antiferromagnetically coupled through the nonmagnetic layers; the first and fifth ferromagnetic layers consist of a Co-based alloy or a three-layered film of a Co-based alloy/a Nixe2x80x94Fe alloy/a Co-based alloy; and a tunnel current is flowed between the first ferromagnetic layer and the fifth ferromagnetic layer.
In the magnetoresistive elements of the present invention, the thickness of the Co-based alloy or the above three-layered film of the Co-based alloy/the Nixe2x80x94Fe alloy/the Co-based alloy is preferably 1 to 5 nm.
A magnetic memory device of the present invention comprises a transistor or a diode, and any one of the first to fourth magnetoresistive element.
The magnetic memory device of the present invention comprises a transistor or a diode and the first or third magnetoresistive element, and at least the uppermost antiferromagnetic layer in the magnetoresistive element constitutes a part of a bit line.
Another magnetic memory device of the present invention comprises a first magnetization pinned layer whose magnetization direction is pinned, a first dielectric layer, a magnetic recording layer whose magnetization direction is reversible, a second dielectric layer, and a second magnetization pinned layer whose magnetization direction is pinned; the magnetic recording layer comprises the three-layered film of a magnetic layer, a nonmagnetic layer and a magnetic layer, two magnetic layers constituting the three-layered film being antiferromagnetically coupled; and magnetization directions of the magnetization pinned layers in regions in contact with the dielectric layer are substantially anti-parallel to each other.
Still another magnetic memory device of the present invention comprises, a first magnetization pinned layer whose magnetization direction is pinned, a first dielectric layer, a magnetic recording layer whose magnetization direction is reversible, a second dielectric layer, and a second magnetization pinned layer whose magnetization direction is pinned; the magnetic recording layer comprising a three-layered film of a magnetic layer, a nonmagnetic layer and a magnetic layer, the two magnetic layers constituting the three-layered film being antiferromagnetically coupled; the second magnetization pinned layer comprising a three-layered film of a magnetic layer, a nonmagnetic layer and a magnetic layer, the two magnetic layers constituting the three-layered film being antiferromagnetically coupled; a length of the first magnetization pinned layer being formed longer than those of the second magnetization pinned layer and the magnetic recording layer; and magnetization directions of the two magnetization pinned layers in regions in contact with the dielectric layer being substantially anti-parallel to each other.
A method for writing information to the above magnetic memory devices comprises steps of: supplying the magnetic recording layer with a spin current through the first or second magnetization pinned layer; and flowing a current in a wire for writing so as to apply a current magnetic field to the magnetic recording layer.
Still another magnetoresistive element of the present invention comprises a ferromagnetic double tunnel junction having a stacked structure of a first antiferromagnetic layer/a first ferromagnetic layer/a first tunnel insulator/a second ferromagnetic layer/a first nonmagnetic layer/a third ferromagnetic layer/a second nonmagnetic layer/a fourth ferromagnetic layer/a second tunnel insulator/a fifth ferromagnetic layer/a second antiferromagnetic layer; the second and third ferromagnetic layers are antiferromagnetically coupled through the first nonmagnetic layer; and the third and fourth ferromagnetic layers are antiferromagnetically coupled through the second nonmagnetic layer.
Additional objects and advantages of the invention will be set forth in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. The objects and advantages of the invention may be realized and obtained by means of the instrumentalities and combinations particularly pointed out hereinafter.